22 research outputs found
Unraveling the Replication Machine from Negative-Stranded RNA Viruses
AbstractThe atomic structure of the Borna-disease virus nucleocapsid protein represents the first detailed structural information for such essential element in the negative-stranded RNA virus replication machine
An Sl(3,R) multiplet of 8-dimensional type II supergravity theories and the gauged supergravity inside
The so-called ``massive 11-dimensional supergravity'' theory gives, for one
Killing vector, Romans' massive 10-dimensional supergravity in 10 dimensions,
for two Killing vectors an Sl(2,Z) multiplet of massive 9-dimensional
supergravity theories that can be obtained by standard generalized dimensional
reduction type IIB supergravity and has been shown to contain a gauged
supergravity. We consider a straightforward generalization of this theory to
three Killing vectors and a 3\times 3 symmetric mass matrix and show that it
gives an Sl(3,Z) multiplet of 8-dimensional supergravity theories that contain
an SO(3) gauged supergravity which is, in some way, the dual to the one found
by Salam and Sezgin by standard generalized dimensional reduction.Comment: Latex2e, 20 pages, reference correcte
Supersymmetric Brane-Worlds
We present warped metrics which solve Einstein equations with arbitrary
cosmological constants in both in upper and lower dimensions. When the
lower-dimensional metric is the maximally symmetric one compatible with the
chosen value of the cosmological constant, the upper-dimensional metric is also
the maximally symmetric one and there is maximal unbroken supersymmetry as
well. We then introduce brane sources and find solutions with analogous
properties, except for supersymmetry, which is generically broken in the
orbifolding procedure (one half is preserved in two special cases), and analyze
metric perturbations in these backgrounds In analogy with the D8-brane we
propose an effective -brane action which acts as a source for the
RS solution. The action consists of a Nambu-Goto piece and a Wess-Zumino term
containing a -form field. It has the standard form of the action
for a BPS extended object, in correspondence with the supersymmetry preserved
by the solution.Comment: 13 pages, Latex2e. Corrected and shortened version to appear in Phys.
Lett.
S-Duality, SL(2,Z) Multiplets and Killing Spinors
The S-duality transformations in type IIB string theory can be seen as local
U(1) transformations in type IIB supergravity. We use this approach to
construct the multiplets associated to supersymmetric backgrounds of
type IIB string theory and the transformation laws of their corresponding
Killing spinors.Comment: 13 pages, Harvma
Godel Spacetimes, Abelian Instantons, the Graviphoton Background and other Flacuum Solutions
We study the relations between all the vacua of Lorentzian and Euclidean
d=4,5,6 SUGRAs with 8 supercharges, finding a new limiting procedure that takes
us from the over-rotating near-horizon BMPV black hole to the Godel spacetime.
The timelike compactification of the maximally supersymmetric Godel solution of
N=1,d=5 SUGRA gives a maximally supersymmetric solution of pure Euclidean
N=2,d=4 with flat space but non-trivial anti-selfdual vector field flux
(``flacuum'') that, on the one hand, can be interpreted as an U(1) instanton on
the 4-torus and that, on the other hand, coincides with the graviphoton
background shown by Berkovits and Seiberg to produce the C-deformation
introduced recently by Ooguri and Vafa. We construct flacuum solutions in other
theories such as Euclidean type IIA supergravity.Comment: Latex file, 33 pages, 2 eps figures. Some misprints corrected and teh
KG4 symmetry superalgebra adde
Supersymmetry of Massive D=9 Supergravity
By applying generalized dimensional reduction on the type IIB supersymmetry
variations, we derive the supersymmetry variations for the massive
9-dimensional supergravity. We use these variations and the ones for massive
type IIA to derive the supersymmetry transformation of the gravitino for the
proposed massive 11-dimensional supergravity.Comment: 13 page
Gauged/Massive Supergravities in Diverse Dimensions
We show how massive/gauged maximal supergravities in 11-n dimensions with
SO(n-l,l) gauge groups (and other non-semisimple subgroups of Sl(n,R)) can be
systematically obtained by dimensional reduction of ``massive 11-dimensional
supergravity''. This series of massive/gauged supergravities includes, for
instance, Romans' massive N=2A,d=10 supergravity for n=1, N=2,d=9 SO(2) and
SO(1,1) gauged supergravities for n=2, and N=8,d=5 SO(6-l,l) gauged
supergravity. In all cases, higher p-form fields get masses through the
Stuckelberg mechanism which is an alternative to self-duality in odd
dimensions.Comment: Latex2e file, 32 page
Interfacial instabilities of a fluid annulus in a rotating Hele-Shaw cell
We have studied the interfacial instabilities experienced by a liquid annulus as it moves radially in a circular Hele-Shaw cell rotating with angular velocity Omega. The instability of the leading interface (oil displacing air) is driven by the density difference in the presence of centrifugal forcing, while the instability of the trailing interface (air displacing oil) is driven by the large viscosity contrast. A linear stability analysis shows that the stability of the two interfaces is coupled through the pressure field already at a linear level. We have performed experiments in a dry cell and in a cell coated with a thin fluid layer on each plate, and found that the stability depends substantially on the wetting conditions at the leading interface. Our experimental results of the number of fingers resulting from the instability compare well with the predictions obtained through a numerical integration of the coupled equations derived from a linear stability analysis. Deep in the nonlinear regime we observe the emission of liquid droplets through the formation of thin filaments at the tip of outgrowing fingers
Low viscosity contrast fingering in a rotating Hele-Shaw cell
We study the fingering instability of a circular interface between two immiscible liquids in a radial Hele-Shaw cell. The cell rotates around its vertical symmetry axis, and the instability is driven by the density difference between the two fluids. This kind of driving allows studying the interfacial dynamics in the particularly interesting case of an interface separating two liquids of comparable viscosity. An accurate experimental study of the number of fingers emerging from the instability reveals a slight but systematic dependence of the linear dispersion relation on the gap spacing. We show that this result is related to a modification of the interface boundary condition which incorporates stresses originated from normal velocity gradients. The early nonlinear regime shows nearly no competition between the outgrowing fingers, characteristic of low viscosity contrast flows. We perform experiments in a wide range of experimental parameters, under conditions of mass conservation (no injection), and characterize the resulting patterns by data collapses of two characteristic lengths: the radius of gyration of the pattern and the interface stretching. Deep in the nonlinear regime, the fingers which grow radially outwards stretch and become gradually thinner, to a point that the fingers pinch and emit drops. We show that the amount of liquid emitted in the first generation of drops is a constant independent of the experimental parameters. Further on there is a sharp reduction of the amount of liquid centrifugated, punctuated by periods of no observable centrifugation